User Profile

Hello everyone! We are developing a health app where we need to keep track of user's accelerometer in real time. Which means we need to read accelerometer values all the time, when the screen is on and off. Is there a better way to do it other then initiating a HKWorkoutSession? If not, what activityType should we use for HKWorkoutConfiguration? Another question is: I noticed in some apps when you start an activity and the sensor on the back is flashing there is a thing that when you close the app by pressing the crown and turn off the screen when you turn it back on that app with activity running is presented. Like I never closed it. How do you do that? What is it connected to? I hope that all makes sense and thank you for taking your time to read respond!